“Cold Tropics”: Permafrost Existence and Thickness on Eastern Nevado Coropuna (Southern Peruvian Andes) Revealed by Ground‐Penetrating Radar and Geoelectrical Soundings

The existence of permafrost was explored at tropical latitude on Nevado Coropuna (southern Peruvian Andes) using a combination of ground-penetrating radar (GPR) and vertical electrical sounding (VES) in order to strengthen the mutual validation of data processing and interpretation. Two GPR surveys (25 and 10 MHz unshielded antennas) and two VES measurements were conducted on the unglaciated eastern flank of the mountain, exploring the internal structure of a rock glacier and the debris slope adjacent to the rock glacier. According to several longitudinal and transverse GPR profiles, a 15–20 m thick permafrost layer was identified beneath 2–4 m thick unfrozen sediments in the rock glacier and adjacent debris slope. The permafrost layer shows a homogeneous distribution within the rock glacier's subsurface, with maximum values reached in the middle and frontal areas, where radar data indicate the potential existence of buried massive ice. This evidence corresponds to the presence of a well-developed frozen layer with significant lateral continuity and a minimum discontinuous permafrost limit in this area at 5090 m.a.s.l. The extensive unglaciated area at this altitude and with a similar aspect indicates that Nevado Coropuna hosts one of the largest tropical permafrost areas in the world, emphasizing the strategic importance of assessing the extent of the permafrost water reservoir in this Andean region, which is affected by dry conditions and prolonged drought.